Step 5: A Four-Way Switch in the Circuit

Step 6: Turning the Light "Off"

In this graphic the four-way switch has been moved to its other toggle position. There is a pathway for the electricity through the four-way switch, ...

While a three-way switch is very simple to many who visit Instructables.com, it is a mystery to many others. Understanding how the circuit works satisfies curiosity. It can also help to diagnose a three-way switch that does not work because someone wired the circuit incorrectly.

This is the basic circuit for a three-way switch. The gray circle represents a light bulb controlled by the two switches. It is gray because it is "off." The two lines ending near the left side of the drawing go to a power source, like the circuit breaker panel in your house.

The green rectangles represent the switches. Notice that one conductor comes into each switch, but two go out. When the toggle is thrown the pathway inside the switch shifts from one of the out conductors to the other.

Here you can see that electricity can flow along the upper wire through the first switch, but its pathway is broken at the second switch and the light remains "off."

Step 1: The Light Comes "On"

In this graphic someone has entered a room and flipped the switch at the right of the frame. The electricity that flows through the first switch now finds a pathway through the second switch and the light is "on" as represented by the yellow bulb.

Step 2: Turning the Light "Off" from another Switch

Let us assume this is a large room. The person who entered and turned the light "on" with the switch at the right of the drawing decides to leave the room near the switch at the left of the graphic. He or she flips the switch to its other position. This makes a break in the circuit again, and the light is now "off."

In my mind I like to think of three-way switches as like a construction zone on a four lane highway. If one set of lanes is closed, a crossover in the median moves traffic over to one of the lanes normally used for traffic going in the other direction. If there were no second crossover, traffic would stop. But, the second crossover brings traffic back to the original lanes and traffic continues to flow.

A 4-way switch could be used as a 2-way or on/off switch. But, if by common you mean the white wire or neutral, do not connect it to the switch, or you will get a direct short between the hot and the neutral. An on/off switch is installed in the path of the black or hot wire.

Great explanation but I must throw this one out there. An instructor presented His class with a Garage having 1 recpt. & one keyless (bare bulb socket), and switch for control. 3 conductors connected Garage to House where opposite 3-way switch is located. Garage recpt. is constantly hot, Garage light controlled by 2 switches in House and Garage. Using only existing 3 conductors how does this work? I must add, no it doesn't meet accepted code requirements. If someone can schematic this out, I'll dig out my old notes to verify because I have forgotten how you cheat this in since I took the course 30 years ago. My instructor was an Electrical inspector in his 70s who took great pleasure in tormenting his protege's with problems such as this even when they obviously were against common code basics. In his time though a grounding, non-current carrying conductor was unheard of except in Submarines.

The image in my response below shows a "hot 3-way switch" circuit. I believe it is what Zapp had in mind. I found it on the Internet by searching for "hot 3-way." When I was my father's helper back in the 1960s, he often spoke of these. I have never seen one.

thank you whoever did this thing on 4 way switches. i figured a 4 way switch had 4 terminals, but i couldn't figure how it actually "switched" without leaving a completely open circuit. i think you made 4 way switches' concept very easy to understand. thanks again, josh -south carolina (united states)

You are welcome. I am glad it was easy to grasp. My father did electrical work and farmed in a rural area of Iowa. I was his helper all through junior high to college. I have 57 other Instructables, all of which are something practical. You might be interested in some of those, too.

Thats not how they are wired here in NZ. Also if there are 2 switches it gets called a 2 way switch here since there are 2 switches. What they do is wire one of the switches normally, to add 2 way capabilities a piece of 3 conductor cable is taken from there to the other switch location, and 1 is connected to 1, 2 to 2, and C to C - the cable is red/white/blue since they are allowable phase colours (yellow used to be but in harmonisation with Aussie it was decided not to be since its easy to mistake for a green/yellow earth) Anyway, then the power is connected to the 1 terminal of one switch, and the 2 terminal takes the power out to the lamp. This is done since its normal that the power goes in and out of the same flushbox rather then taking a single conductor to the other end. It is sometimes done the way described with a wire joiner taking the cable to the C of the remote switch to the cable out to the light, but thats not how new installs are done.

I am not sure why we call them 3-way and 4-way switches in the USA, but we sure do. My graphic is more of a schematic than a plan for routing wires. Certainly we most often use three strand cables between the switches. What connects to what depends on the layout of the building and where the light, the switches, and the circuit breaker are in relation to one another.

I do not think you are/were alone by far. My father did electrical work and I often went with him as his assistant. I have met plenty of people who puzzled over how these things work. It is not that hard, once you grasp the concept. Thanks for your comment.

Thank you. If you like being able to understand what may have been mysterious, wait until you amaze your family and friends by making a 3-way switch circuit work that never worked before. You will achieve rock star status. I think, too, the idea of comparing these circuits to a crossover at an Interstate construction zone makes it clear in one's mind.

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Bio:I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my...read more »